Mixing Subsidised Diesel and Dex: A Clever Solution or a Boomerang?

JAKARTA – Amid ongoing adjustments to fuel prices, the practice of mixing fuels among diesel vehicle users occasionally occurs. This method is often seen as a middle ground between cost efficiency and maintaining fuel quality.

At first glance, the approach seems reasonable: not fully relying on expensive fuel, but also not depending entirely on subsidised solar.

Dosen from Universitas Gadjah Mada (UGM), Jayan Sentanuhady, explains that technically, mixing two types of diesel fuel is not dangerous for the engine.

“Generally safe. But it’s best not to do it,” Jayan told Kompas.com on Monday (4/5/2026).

He added that the result of the mixture will not provide the best quality.

“If mixed, the quality is somewhere between the two types,” he said.

Nevertheless, he reminds users to understand the consequences of this decision, especially regarding engine performance.

“That means the performance will also not be as good as using fuel that fully matches the specifications,” Jayan stated.

Dex, which has a higher cetane number and lower sulphur content, is designed to produce cleaner and more efficient combustion. When mixed with subsidised solar, these characteristics are diminished.

As a result, engine response may feel less than optimal, fuel efficiency may not be fully achieved, and exhaust emissions could potentially increase compared to using pure Dex.

In the long term, using fuel with inconsistent quality can also affect components of the fuel system, such as injectors and combustion chambers. Although not immediately damaging, this condition could accelerate maintenance requirements.